What is the minimum percentage of incombustible material required after rock dust application in return entries?

The minimum percentage of incombustible material required after rock dust application in return entries is indeed eighty percent (80%). This requirement is established to enhance safety in underground mining operations by reducing the potential for fire and explosion. Rock dust, when applied correctly, serves to inert the coal dust present in the mine environment, significantly minimizing the risk of a combustive event.

Maintaining a high percentage of incombustible material ensures that the risk of fire or explosion from coal dust is effectively mitigated. This guideline reflects advances in safety practices and emphasizes the importance of preventative measures in maintaining a safe working environment for miners. Additionally, the 80% threshold has been demonstrated to be effective in providing a significant buffer against potential ignition sources, fostering an environment where the likelihood of fire hazards is considerably reduced.

Other choices represent lower thresholds and do not satisfy the current safety standards established for underground mining practices, which prioritize the health and safety of personnel working in these potentially hazardous conditions.